Electroluminescent element and method of producing the same

ABSTRACT

An electroluminescent element and method for manufacturing the same including an anode, a cathode, and a light emitting layer disposed in a plane between the anode and the cathode. The light emitting layer containing a fluorescent first compound, and at least a portion of the light emitting layer also containing a second compound which absorbs a first fluorescence generated by the first compound and emits a second fluorescence of a longer wavelength than the first fluorescence. The concentration of the second compound has a gradient along a thickness direction of the light emitting layer perpendicular to the plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the construction of electroluminescentelements in which light-emitting thin films are used which can beemployed, for example, as displays for lap-top computers, televisionsand mobile communications, and a method for their manufacture.

2. Description of the Related Art

Light-emitting elements in which the electroluminescence of organiccompounds is employed are auto-luminescent and so they have a highvisibility, since they are completely solid elements they have excellentimpact resistance and since they are also characterized by a low drivevoltage they are clearly useful as light emitting elements for varioustypes of display equipment.

Clearly multi-color elements like those seen in Braun tubes (CRT) andliquid crystal displays (LCD) will be required to extend the range ofapplication of the abovementioned organic EL elements as displayelements.

The following methods, for example, were known as means of producingmulti-color display apparatus using EL elements in the past. (1) Methodsin which EL materials which emit light of the three colors red (R),green (G) and blue (B) are arranged in a matrix (Japanese Laid-openPatent Publications Sho.57-157487, Sho.58-145989 and H3-214593 forexample). (2) Methods in which the three primary colors RGB are realizedby combining color filters with EL elements which emit white light(Japanese Laid-open Patent Publications H1-315988, H2-273496, H3-194895for example). (3) Methods in which EL elements which emit blue light andfluorescent conversion elements are combined for conversion to providethe three primary colors RGB (Japanese Laid-open Patent PublicationH3-152897).

However, the methods described under (1) above must have three types oflight emitting material arranged in a very finely divided manner in amatrix and so the technology is complex and the product cannot bemanufactured cheaply, and since the life expectancies of the three typesof light emitting material will generally be quite different there is afurther disadvantage in that there will inevitably be a displacement ofthe color balance with the passage of time. Furthermore, the methodsdescribed in (2) make use of some of the light output from EL elementswhich emit white light using color filters and so there is adisadvantage in that the utilization efficiency of the EL light, whichis to say the conversion efficiency, is low. For example, the white ELlight simply comprises the three primary colors RGB which are of equalintensity and if the colors are obtained from this using color filtersthen at the most only a 33% conversion efficiency can be obtained. Inpractice, when the emission spectrum and visual perception are takeninto consideration then only a much lower conversion efficiency can beobtained. On the other hand, if the three primary colors RGB could beobtained with conversion efficiencies of more than 33% respectively withthe methods described under (3) these would be better methods than thosedescribed under (2) above.

Thus, methods in which fluorescent conversion films are arranged in thelamination direction over the EL elements, thus changing the EL emissioncolor, are known (Japanese Laid-open Patent Publications Sho.63-18139,H3-152897). Since blue is emitted by the organic EL elements, theconversion efficiency can be 100%. Furthermore, an 80% conversionefficiency can be achieved using coumarin 153 as disclosed in JapaneseLaid-open Patent Publication H3-152897 for green. Furthermore, a methodof converting EL element blue light to red with a conversion efficiencyof more than 33% has been disclosed in Japanese Laid-open PatentPublications H8-286033.

Thus, the fluorescent conversion method is superior as a means ofachieving a full color display, but in terms of the actual method ofmanufacture, processes similar to the those for the color filters whichare used conventionally in color liquid crystal display apparatus arerequired to manufacture a fluorescent conversion film and there is aproblem in that this is very expensive.

SUMMARY OF THE INVENTION

The present invention is intended to overcome these weaknesses in theconventional technology. An object of the present invention is toprovide electroluminescent elements with which the emitted light of ablue light emitting organic EL element can be converted to other colorswith a high conversion efficiency of at least 33% and to provide amethod of manufacture whereby these color electroluminescent elementscan be manufactured cheaply using an ink-jet method.

The electroluminescent elements of this invention are characterized inthat they comprise a light emitting layer comprised of a fluorescentfirst compound with is arranged in a plane between a cathode and ananode. A hole injection transport layer comprising a mixture of a secondcompound which absorbs the fluorescence generated by the aforementionedfirst compound and emits a longer wavelength than the aforementionedfluorescence. A compound which has a charge injection/transportationcapacity is arranged between the aforementioned anode and theaforementioned light emitting layer. By this means, the second compoundlayer is arranged on the light output side and so all of the lightemitted from the light emitting layer which is formed by the firstcompound falls on the second compound layer, is absorbed by the secondcompound and discharged after being wavelength converted, and so thecolor purity is high.

If, in this case, the construction is such that the concentration of theaforementioned second compound has a gradient along a thicknessdirection of the light emitting layer perpendicular to the plane and theaforementioned hole injection transport layer then movement of the holesis facilitated and the light emission efficiency is improved.

Furthermore, another electroluminescent element of the invention ischaracterized in that it is comprises a light emitting layer having amixture of a fluorescent first compound and a second compound whichabsorbs the fluorescence emitted by the aforementioned first compoundand emits fluorescence of longer wavelength that the aforementionedfluorescence which is a arranged between an anode and a cathode, and inthat it is established in such a way that the concentration of theaforementioned second compound with respect to the aforementioned firstcompound in the aforementioned light emitting layer varies with agradient along the thickness direction of said light emitting layer.Moreover, such elements are characterized in that the proportions of theaforementioned first compound and the aforementioned second compound arefrom 99.9:0.1 to 90:10. With such constructions, the charge injectedfrom the electrodes reaches the light emitting layer with goodefficiency and so the light emitting layer comprising mainly the firstcompound emits the fluorescence of the first compound and then thisfluorescence and the fluorescence which has been reflected by thecathode is absorbed directly and indirectly with good efficiency by thesecond compound and the second compound emits its own fluorescence. Inthis case there is no distinct interface between the first compound andthe second compound and so direct energy transfer occurs at the sametime as the energy transfer by means of light and the conversionefficiency is improved.

Furthermore, another such element is characterized in that a chargeinjection transport layer is formed between the aforementioned lightemitting layer and the electrodes in the aforementionedelectroluminescent element. With this construction charge injection inthe aforementioned construction is achieved with greater efficiency withthe result that the light emitting efficiency is also improved.

These elements are also characterized in that the first and secondcompounds used in the abovementioned electroluminescent elements areorganic compounds or organometallic compounds. The drive voltage can begreatly reduced in this way.

These elements are also characterized in that the surface of theabovementioned electroluminescent element is subjected to an anti-glaretreatment and/or anti-reflection treatment. The reflected light from thesurface of the electroluminescent element can be reduced or scattered inthis way and so the display becomes easier to see.

Moreover, these elements are characterized in that they are providedwith a means whereby the layer structure of the electroluminescentelement itself is isolated from the surroundings. Each layer isprotected by this means and the durability is improved.

Next, the method for the manufacture of electroluminescent elementswhere a light emitting layer is sandwiched between an anode and acathode is characterized in that it is provided with a process whereby atransparent anode is formed on a transparent substrate, a processwhereby a hole injection transport layer is formed using a mixture ofcompound which has a charge injection/transportation function with asecond compound which absorbs the fluorescence produced by a fluorescentfirst compound and emits fluorescence of a longer wavelength than saidfluorescence, a process whereby said first compound is deposited as afilm on the whole of the surface of the aforementioned hole injectiontransport layer using a solvent of which the compatibilities in respectof the aforementioned first compound and the aforementioned secondcompound are controlled and in which said second compound in theaforementioned hole injection transport layer permeates into said firstcompound layer and a light emitting layer is formed, and a processwhereby a cathode is formed on said light emitting layer. With thismethod the hole injection transport layer can be patterned and so it ispossible to avoid short circuiting between the anode and cathode even ifsubstances which have good charge injection properties which have a highelectrical conductivity are used for the hole implanting material.Furthermore, the fluorescent conversion substance can also be patternedat the same time and so full color and high efficiencyelectroluminescent elements can be manufactured using the best materialswith a simple process.

Next, there is a method for the manufacture of electroluminescentelements in which a light emitting layer is disposed in a plane betweenan anode and a cathode. The method for manufacture include; a processwhereby a transparent anode is formed on a transparent substrate, aprocess whereby a film of the first fluorescent compound is formed overthe whole surface, a process whereby a second compound is applied as asolution and absorbs the fluorescence emitted by a fluorescent firstcompound and emits fluorescence of a longer wavelength than saidfluorescence, said second compound is caused to permeate into theaforementioned first compound and a light emitting layer is formedhaving a gradient along a thickness direction of the light emittinglayer perpendicular to the plane, and a process whereby a cathode isformed on the aforementioned light emitting layer.

Furthermore, there is a method of manufacture which provides; a processwhereby a transparent anode is formed on a transparent substrate, aprocess whereby a second compound is applied as a solution and absorbsthe fluorescence emitted by a fluorescent first compound and emitsfluorescence of a longer wavelength than said fluorescence, a processwhereby the aforementioned first compound is formed as a film over thewhole surface using a solvent of which the compatibilities with respectto the aforementioned first compound and the aforementioned secondcompound are controlled and said second compound permeates into saidfirst compound and a light emitting layer is formed, and a processwhereby a cathode is formed on the aforementioned light emitting layer.By means of these methods of manufacture it is possible to easilyachieve changes in the emission color of adjoining picture elements andto reduce the manufacturing costs. Furthermore, in those cases where thefirst compound is discharged from an ink-jet head, the concentrationgradient in the thickness direction can be controlled by controlling thecompatibility with the second compound. It is possible by this means tomanufacture electroluminescent elements in which the gradient is matchedto the characteristics of the first compound and the second compound.

Next, there is a method for the manufacture of electroluminescentelements in which a light emitting layer is sandwiched between an anodeand a cathode in which there are provided a process whereby atransparent anode is formed on a transparent substrate, a processwhereby a light emitting film is formed by mixing a fluorescent firstcompound and a second compound which absorbs the fluorescence emitted bysaid first compound and emits fluorescence of a longer wavelength thansaid fluorescence and the mixture is applied as a solution, and aprocess in which a cathode is formed on the aforementioned lightemitting layer. With this method it is possible to manufacture fullcolor electroluminescent elements with a very simple process and verycheaply.

Next, there is a method for the manufacture of electroluminescentelements in which a light emitting layer is sandwiched between an anodeand a cathode in which there are provided a process whereby atransparent anode is formed on a transparent substrate, a processwhereby a light emitting film is formed by attaching a fluorescent firstcompound as a solution, and a process whereby a cathode is formed on theaforementioned light emitting layer. With this method it is possible tomanufacture full color electroluminescent elements with a very simpleprocess and very cheaply.

A process whereby a hole injection transport layer is formed between theanode and the light emitting layer may be provided in theelectroluminescent elements as a means of resolving the problemsdescribed above. It is possible to manufacture bright elements in whichcharge implantation is achieved efficiently by forming a hole injectiontransport later.

There is a method of manufacture in which the application of theabovementioned solution in an electroluminescent element is carried outby discharging said solutions onto the surface to which they are to beattached using an ink-jet system as a means of resolving the problemsdescribed above. With an ink-jet system, fluid compounds can beintroduced selectively into each picture element without wastingmaterial.

There is a method wherein banks are formed between picture elements inorder to divide the aforementioned picture elements. In this way it ispossible to prevent cross-contamination between adjacent pictureelements when forming a film with the ink-jet method and to preventdiffusion of the organic molecules between adjacent picture elementsafter the elements have been produced. Furthermore, there is no crossingof the emission colors between picture elements and brilliant lightemission can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple cross sectional view of the electroluminescentelements of Embodiment 1 of the invention;

FIG. 2 is a simple cross sectional view of the electroluminescentelements of Embodiment 2 of the invention;

FIG. 3 is a simple cross sectional view of the electroluminescentelements of Embodiment 3 of the invention;

FIG. 4 is a simple cross sectional view of the electroluminescentelements of Embodiment 4 of the invention;

FIG. 5 is a simple cross sectional view of the electroluminescentelements of Embodiment 5 of the invention;

FIG. 6 is a simple cross sectional view of the electroluminescentelements of Embodiment 6 of the invention;

FIG. 7 is a simple cross sectional view of the electroluminescentelement of Embodiment 7 of the invention;

FIG. 8 is a perspective view of the drive circuit of theelectroluminescent element of Embodiment 9 of the invention; and

FIG. 9 is a drawing of the drive waveform used when driving theelectroluminescent element of Embodiment 9 of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

This embodiment shows and example of an electroluminescent elementcomprising a transparent substrate, a transparent anode or anode array,a hole injection transport layer comprising the second compound and acompound which has a hole injection transport function, a light emittinglayer comprising the first compound and a cathode or cathode array, andthe second compound concentration has a gradient between the holeinjection transport layer and the light emitting layer.

A simple cross sectional drawing of the electroluminescent element ofthis embodiment is shown in FIG. 1. As shown in FIG. 1, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, a hole injection transport andfluorescent conversion layer 5, banks 4, a concentration gradient layer3, a light emitting layer 2 and a cathode 1. The anode 6 is an anodearray which had been formed by patterning for each of the pictureelements on the transparent substrate 7. The hole injection transportand fluorescent conversion layer 5 is a layer which has been formed bymixing a second compound which absorbs the fluorescence emitted by thefirst compound from which the light emitting layer is formed and emitsfluorescence of a longer wavelength (fluorescent conversion layer) and acompound which has a charge injection/transportation capacity. The banks4 are constructed as partitions to divide the picture elements. Thelight emitting layer 2 is comprised of the aforementioned fluorescentfirst compound. The cathode 1 has a construction which can be used as acommon cathode.

An electroluminescent element which has been made in this way hasemitted light of the color corresponding to the fluorescence of thesecond compound, and when coumarin 6 is used for the second compound thelight emitting efficiency is 1.2 lm/W and the maximum brightness is13,000 cd/m². The electroluminescent element has the same efficiency asin the case of the vapor deposition method indicated below.

The same effect can be realized even if active elements such as TFTelements are formed to form the anode and large capacity displays arepossible.

An electron injection transport layer may be formed between the lightemitting layer and the cathode in this embodiment, and metal organiccomplexes such as aluminum quinolinium complexes, for example, andoxadiazole complexes, for example, can be used.

The same effect can be realized even if active elements such as TFTelements are formed to form the anode and large capacity displays arepossible.

The method by which the abovementioned electroluminescent element wasmanufactured is described below. In the method by which theelectroluminescent element which had a light emitting layer sandwichedbetween an anode and a cathode was manufactured, the transparent anodeor anode array was formed on the transparent substrate. Next, the holeinjection transport layer was formed by discharging a suitable solutionby means of an ink-jet head onto the picture elements on the anode oranode array. The solution is a mixture of the second compound and thecompound which has a charge injection transport capacity. Theaforementioned light emitting layer was generated by forming the firstcompound into a film over the whole surface using a solvent in which thecompatibility of the second compound is controlled and causing thesecond compound to permeate into the first compound layer. Finally, thecathode or cathode array was formed over the top.

First of all, ITO was EB vapor deposited, vapor deposited or sputteredas a transparent electrode onto a clean glass substrate (transparentsubstrate 7) and the anode 6 was formed by patterning. Moreover, thebanks 4 were formed as shown in FIG. 1 using a photosensitive polyimide.Next, after subjecting the surface of the substrate to treatment withultraviolet radiation of wavelength 174 nm, a solution comprised of amixture of the hole injection transport substance and the secondcompound was discharged onto the anode surface using an ink-jet head anddried forming the hole injection transport and fluorescent conversionlayer 5 of thickness 50 nm. The first compound which formed the lightemitting layer was printed in the form of a solution with a roll-coateronto the hole injection transport layer and dried to form the lightemitting layer 2 of thickness 50 nm. As a result of this process, aconcentration gradient layer 3 was formed between the hole injectiontransport and fluorescent conversion layer 5 and the light emittinglayer 2. Next, an Mg:Ag (10:1) alloy was EB vapor deposited, vapordeposited or sputtered on using a mask to form the cathode 1. Finally,the element was molded under an inert gas in a degassed epoxy resin as ameans of isolating the element from the surroundings. Other thermosetresins, ultraviolet setting resins or polysiloxane containing siliconresins, for example, can be used in the same way provided that they areable to keep out air and moisture and do not invade the organic films.

TPD (Chemical Formula 1) was used for the hole injection material, butm-MTDATA (Chemical Formula 2), porphin compounds such as copperphthalocyanine, NPD (Chemical Formula 3), TAD (Chemical Formula 4),polyvinylcarbazole and derivatives of these compounds, for example, canbe used in the same way provided that they have a charge injectioncapacity. Also, these compounds may have a laminated structure. Perylenewas used for the second compound red wavelength conversion and coumarin6 was used for the green wavelength conversion. Moreover, DCM1 (ChemicalFormula 5), quinacridone derivatives, rubulene, DCJT (Chemical Formula6) and Nile Red, for example, can be used for the second compound.

DPVBi (Chemical Formula 7) was used for the first compound, but1,1,4,4-tetraphenylbutadiene, oxadiazole derivatives, azomethine zinccomplex, Balq (Chemical Formula 8), polyvinylcarbazole and derivativesof these compounds can be used provided that they have a similar effect.

Screen printing methods, spin coating methods where a film is formedwith a solution, and methods where the second compound is diffused intothe light emitting layer, for example, can be used instead of the methoddescribed here for forming the light emitting layer.

The same effects can be realized even if active elements such as TFTelements are formed for forming the anode and high capacity displays arepossible.

Materials which have a low work function can be used instead of Mg:Agfor forming the cathode and, for example, magnesium, aluminum, andalkali and alkaline earth metals such as lithium and calcium, and alloysin which these metals are used, can be used for this purpose.

Embodiment 2

In this embodiment there is no concentration gradient of the secondcompound between the light emitting layer and the hole injectiontransport layer in the structure of embodiment 1.

A simple cross sectional drawing of the electroluminescent element ofthis embodiment is show in FIG. 2. As shown in FIG. 2, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, a fluorescent conversion layer 8,the banks 4, a light emitting layer 2 and a cathode 1. Theelectroluminescent element of embodiment 2 differs from embodiment 1 inthat there is no concentration gradient layer 3. This is because thefirst compound is attached by vapor deposition instead of by coating thefirst compound in the form of a solution.

An electroluminescent element which has been made in this way hasemitted light of the color corresponding to the fluorescence of thesecond compound, and when coumarin 6 is used for the second compound thelight emitting efficiency is 1.2 lm/W and the maximum brightness is13,000 cd/m², and it has roughly the same efficiency as when the lightemitting layer was formed by printing as in the first embodiment.

An electron injection transport layer may be formed between the lightemitting layer and the cathode in this embodiment using, for example,metal organic complexes such as aluminum quinolinium complexes, andoxadiazole complexes.

The same effects can be realized even if active elements such as TFTelements are formed for forming the anode and high capacity displays arepossible.

The method by which the abovementioned electroluminescent element wasmanufactured is described below. First of all, ITO was EB vapordeposited, vapor deposited or sputtered as a transparent electrode ontoa clean glass substrate (transparent substrate 7) and the anode 6 wasformed by patterning. Moreover, the banks 4 were formed as shown in FIG.2 using a photosensitive polyimide. Next, after subjecting the surfaceof the substrate to treatment with ultraviolet radiation of wavelength174 nm, a solution comprising a mixture of the hole injection transportsubstance and the second compound was discharged onto the anode surfaceusing an ink-jet head and dried forming the fluorescent conversion layer8 having a thickness of 50 nm. The first compound which formed the lightemitting layer 2 was vapor deposited using the vacuum vapor depositionmethod to a film thickness of 50 nm on the hole injection transport andwavelength converting layer 8. Next, an Mg:Ag (10:1) alloy was EB vapordeposited, vapor deposited or sputtered on to form the cathode 1. Next,the electroluminescent element was molded in epoxy resin.

Embodiment 3

This embodiment shows an example of an electroluminescent elementcomprising a transparent substrate, a transparent anode or anode array,a light emitting layer, and a cathode or cathode array, and theaforementioned light emitting layer comprises a mixture of the firstcompound and the second compound and, moreover, the concentration of thesecond compound with respect to the first compound has a gradient in thethickness direction of the aforementioned light emitting layer.

A simple cross sectional drawing of the electroluminescent element ofthis embodiment is show in FIG. 3. As shown in FIG. 3, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, the banks 4, a concentrationgradient layer 3, a light emitting layer 2 and a cathode 1. It differsfrom embodiment 1 in that there is no hole injection/transporting andfluorescent conversion layer.

An electroluminescent element which has been made in this way hasemitted light of the color corresponding to the fluorescence of thesecond compound, and when coumarin 6 is used for the second compound thelight emitting efficiency was 0.1 lm/W and the maximum brightness was150 cd/m².

An electron injection transport layer may be formed between the lightemitting layer and the cathode in this embodiment using, for example,metal organic complexes such as aluminum quinolinium complexes, andoxadiazole complexes.

The same effect can be realized even if active elements such as TFTelements are formed to form the anode and large capacity displays arepossible.

The method by which the abovementioned electroluminescent element wasmanufactured is described below. This embodiment shows an example of anelectroluminescent element in which the aforementioned light emittinglayer comprises a mixture of the first compound and a second compoundwhich absorbs the fluorescence which is emitted by the aforementionedfirst compound and emits fluorescence of a longer wavelength that theaforementioned fluorescence, and the concentration of the secondcompound with respect to the first compound in the aforementioned lightemitting layer has a gradient in the thickness direction of theaforementioned light emitting layer.

First of all, ITO was EB vapor deposited, vapor deposited or sputteredas a transparent electrode onto a clean glass substrate (transparentsubstrate 7) and the anode 6 was formed by patterning. The banks 4 wereformed as shown in FIG. 3 using a photosensitive polyimide. Next, aftersubjecting the surface of the substrate to treatment with ultravioletradiation of wavelength 174 nm, a film of the second compound was formedon the electrode surface by discharging the compound in the form of asolution within the banks using the ink-jet method and the film wasdried. Next, the first compound was discharged in the form of a solutionwith an ink-jet head, using a solvent which was compatible with thesecond compound, and dried forming the light emitting layer 2 ofthickness 50 nm. As a result of this process the second compound wasmixed with the first compound to form the concentration gradient layer3. Next, an Mg:Ag (10:1) alloy was EB vapor deposited, vapor depositedor sputtered on to form the cathode 1. Finally, the electroluminescentelement was molded under an inert gas in a degassed epoxy resin as ameans of isolating the element for the surroundings.

The mixing ratio of the first and second compounds (proportional to thefilm thickness with the same concentration) is preferably within therange from 99.9:0.1 to 90:10. The light emitting efficiency is markedlyreduced outside this range.

Perylene was used for the red long wavelength conversion material andcoumarin 6 was used for the green long wavelength conversion material assecond compound, but DCM1, quinacridone, rubulene, DCJT, Nile Red andderivatives of these compounds can be used for second compound.Polyvinylcarbazole was used for the first compound, but DPVBi,1,1,4,4-tetraphenylbutadiene, oxadiazole, azomethine zinc complex, Balqand derivatives of these compounds can be used provided that they have asimilar effect. The first compound can be applied using a printingmethod rather than by being formed into a film using the ink-jet method.

The same effects can be realized even if active elements such as TFTelements are formed for forming the anode and high capacity displays arepossible.

Materials which have a low work function can be used instead of Mg:Agfor forming the cathode and, for example, magnesium, aluminum, andalkali and alkaline earth metals such as lithium and calcium, and alloysin which these metals are used, can be used for this purpose.

Embodiment 4

This embodiment is an example where a hole injection transport layer isformed in Embodiment 3. A simple cross sectional drawing showing thestructure of this embodiment is shown in FIG. 4. As shown in FIG. 4, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, a hole injection transport layer 9,banks 4, a concentration gradient layer 3, a light emitting layer 2 anda cathode 1. It differs from embodiment 3 in that a hole injectiontransport layer 9 is included.

An electroluminescent element which has been made in this way hasemitted light of the color corresponding to the fluorescence of thesecond compound, and when coumarin 6 was used for the second compoundthe light emitting efficiency was 0.4 lm/W and the maximum brightnesswas 300 cd/m².

An electron injection transport layer may be formed between the lightemitting layer and the cathode in this embodiment, metal organiccomplexes such as aluminum quinolinium complexes, for example, andoxadiazole complexes, for example, can be used.

The same effect can be realized even if active elements such as TFTelements are formed to form the anode and large capacity displays arepossible.

The method by which the abovementioned electroluminescent element wasmanufactured is described below. First of all, ITO and EB vapordeposited, vapor deposited or sputtered as a transparent electrode ontoa clean glass substrate (transparent substrate 7) and the anode 6 wasformed by patterning. The banks 4 were formed as shown in FIG. 4 using aphotosensitive polyimide. Next, after subjecting the surface of thesubstrate to treatment with ultraviolet radiation of wavelength 174 nm,a thin film of the NPD of thickness 50 nm was vapor deposited on theanode surface for the hole injection transport layer 9. Subsequently,films of the second compound and of the first compound were producedusing the same procedures as in embodiment 3 (concentration gradientlayer 3, light emitting layer 2). Then an Mg:Ag (10:1) alloy was EBvapor deposited, vapor deposited or sputtered on to form the cathode 1,and the electroluminescent unit was molded in epoxy resin.

Embodiment 5

This embodiment is an example of an electroluminescent elementcomprising a transparent substrate, a transparent anode or anode array,a hole injection transport layer, a first compound layer, a secondcompound layer, and a cathode or cathode array. The second compound hasa concentration gradient between the first compound layer and the secondcompound layer.

A simple cross sectional drawing of the electroluminescent element ofthis embodiment is show in FIG. 5. As shown in FIG. 5, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, a hole injection transport layer 9,the banks 4, a fluorescent material impregnated light emitting layer 10and a cathode 1. It differs for embodiment 4 in that a fluorescentmaterial is impregnated into the light emitting layer.

An electroluminescent element which has been made in this way hasemitted light of the color corresponding to the fluorescence of thesecond compound. When coumarin 6 was used for the second compound thelight emitting efficiency was 0.2 lm/W and the maximum brightness was200 cd/m².

An electron injection transport layer may be formed between the lightemitting layer and the cathode in this embodiment, metal organiccomplexes such as aluminum quinolinium complexes, for example, andoxadiazole complexes, for example, can be used.

The same effect can be realized even if active elements such as TFTelements are formed to form the anode, and large capacity displays arepossible.

The method by which the abovementioned electroluminescent element wasmanufactured is described below. This embodiment shows an example of anelectroluminescent element in which the light emitting layer issandwiched between the electrodes or electrode arrays, and in this casea transparent anode or anode array is formed on a transparent substrate,and then a hole injection transport layer may be formed, and then theaforementioned first compound is formed as a film over the whole surfaceand then the aforementioned second compound is discharged from anink-jet head as an appropriate solution over the aforementioned anode oranode array and the second compound is caused to permeate into the firstcompound layer to form the aforementioned light emitting layer, and thenthe cathode or cathode array is formed over the top.

First of all, ITO was EB vapor deposited, vapor deposited or sputteredas a transparent electrode onto a clean glass substrate (transparentsubstrate 7) and the anode 6 was formed by patterning. The banks 4 wereformed as shown in FIG. 5 using a photosensitive polyimide. Next, aftersubjecting the surface of the substrate to treatment with ultravioletradiation of wavelength 174 nm, a 1:1 mixture of copper phthalocyanineand epoxypropyltriethoxysilane was coated on the surface of theelectrode for the hole injection transport layer 9 and baked at 200° C.to form a layer of thickness 50 nm. Next, a film of the first compoundwas printed in the form of a solution for the light emitting layer anddried to provide a film thickness of 40 nm. Next, a film was formedwithin the banks with the ink-jet method using the second compound inthe form of a solution. The second compound permeated the first compoundand dried to form the fluorescent substance impregnated light emittinglayer 10. Next, an Mg:Ag (10:1) alloy was EB vapor deposited, vapordeposited or sputtered on to form the cathode 1. Finally, theelectroluminescent element was molded in an inert gas with a degassedepoxy resin.

The mixing ratio of the first and second compounds (proportional to thefilm thickness with the same concentration) is preferably within therange from 99.9:0.1 to 90:10. The light emitting efficiency is markedlyreduced outside this range.

Perylene was used as the second compound for the red wavelengthconversion material and coumarin 6 was used for the green wavelengthconversion material, but DCM1, quinacridone, rubulene, DCJT, Nile Redand derivatives of these compounds can be used for the second compound.

Polyvinylcarbazole was used for the first compound, but DPVBi,1,1,4,4-tetraphenylbutadiene, oxadiazole, azomethine zinc complex, Balqand derivatives of these compounds can be used provided that they have asimilar effect.

The same effects can be realized even if active elements such as TFTelements are formed for forming the anode and high capacity displays arepossible.

Materials which have a low work function can be used instead of Mg:Agfor forming the cathode and, for example, magnesium, aluminum, andalkali and alkaline earth metals such as lithium and calcium, and alloysin which these metals are used, can be used for this purpose.

Embodiment 6

This embodiment is an example of an electroluminescent elementcomprising a transparent substrate, a transparent anode or anode array,a hole injection transport layer, a mixed first compound and secondcompound layer, and a cathode or cathode array.

A simple cross sectional drawing of the electroluminescent element ofthis embodiment is shown in FIG. 6. As shown in FIG. 6, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, a hole injection transport layer 9,the banks 4, a fluorescent material admixed light emitting layer 11 anda cathode 1. It differs for embodiment 4 in that a fluorescent materialis admixed in the light emitting layer.

An electroluminescent element which has been made in this way hasemitted light of the color corresponding to the fluorescence of thesecond compound, and when coumarin 6 was used for the second compoundthe light emitting efficiency was 0.08 lm /W and the maximum brightnesswas 150 cd/m².

An electron injection transport layer may be formed between the lightemitting layer and the cathode in this embodiment using, for example,metal organic complexes such as aluminum quinolinium complexes, andoxadiazole complexes.

The same effect can be realized even if active elements such as TFTelements are formed to form the anode, and large capacity displays arepossible.

The method by which the abovementioned electroluminescent element wasmanufactured is described below. This embodiment shows an example of anelectroluminescent element in which the light emitting layer issandwiched between opposed electrodes or electrode arrays, and in thiscase a transparent anode or anode array is formed on a transparentsubstrate, then a hole injection transport layer may be formed, and thenthe aforementioned first compound and the aforementioned second compoundare mixed and discharged in the form of an appropriate solution with anink-jet head over the anode or anode array to form the aforementionedlight emitting layer, and then the cathode or cathode array is formedover the top.

First of all, ITO was EB vapor deposited, vapor deposited or sputteredas a transparent electrode onto a clean glass substrate (transparentsubstrate 7) and the anode 6 was formed by patterning. The banks 4 wereformed as shown in FIG. 6 using a photosensitive polyimide. Next, aftersubjecting the surface of the substrate to treatment with ultravioletradiation of wavelength 174 nm, a 1:1 mixture of copper phthalocyanineand epoxypropyltriethoxysilane was coated on the surface of theelectrode for the hole injection transport layer 9 and this was baked at200° C. to form a layer of thickness 50 nm. Then, the first compound wasprinted in the form of a solution and dried to a film thickness of 40 nmas the light emitting layer. Next, a 99:1 mixture of the first compoundand the second compound was formed into a film within the banks as asolution using the ink-jet method and dried. A light emitting layer 11in which a fluorescent material was admixed was formed in this way.Next, an Mg:Ag (10:1) alloy was EB vapor deposited, vapor deposited orsputtered on to form the cathode 1. The electroluminescent element wasmolded under an inert gas in a degassed epoxy resin as a means ofisolating it from the surroundings.

The mixing ratio of the first and second compounds (proportional to thefilm thickness with the same concentration) is preferably within therange from 99.9:0.1 to 90:10. The light emitting efficiency is markedlyreduced outside this range.

Perylene was used as the second compound for the red wavelengthconversion material and coumarin 6 was used for the green wavelengthconversion material, but DCM1, quinacridone, rubulene, DCJT, Nile Redand derivatives of these compounds can be used for the second compound.

Polyvinylcarbozole was used for the first compound, but DPVBi,1,1,4,4-tetraphenylbutadiene, oxadiazole, azomethine zinc complex, BA1qand derivatives of these compounds can be used provided that they have asimilar effect.

The same effects can be realized even if active elements such as TFTelements are formed for forming the anode and high capacity displays arepossible.

Materials which have a low work function can be used instead of Mg:Agfor forming the cathode and, for example, magnesium, aluminum, andalkali and alkaline earth metals such as lithium and calcium, and alloysin which these metals are used, can be used for this purpose.

Embodiment 7

This embodiment is an example of a method for the manufacture of anelectroluminescent element which has a light emitting layer sandwichedbetween opposed electrodes or electrode arrays in which a transparentanode or anode array is formed on a transparent substrate, a holeinjection transport layer may be formed, and then the aforementionedlight emitting layer is formed by discharging as an appropriate solutionwith an ink-jet head a first compound on the anode or anode array andthen forming a cathode or cathode array over the top.

A simple cross sectional drawing of an electroluminescent element ofthis embodiment is shown in FIG. 7. As shown in FIG. 7, theelectroluminescent element of this embodiment is furnished with atransparent substrate 7, an anode 6, a hole injection transport layer 9,the banks 4, a light emitting layer 2 and a cathode 1. It differs fromthe abovementioned embodiment in that a fluorescent first compound isused for the light emitting layer.

The method of manufacture of an electroluminescent element is describedbelow. First of all, ITO was EB vapor deposited, vapor deposited orsputtered as a transparent electrode onto a clean glass substrate(transparent substrate 7) and the anode 6 was formed by patterning. Thebanks 4 were formed as shown in FIG. 6 using a photosensitive polyimide.Next, after subjecting the surface of the substrate to treatment withultraviolet radiation of wavelength 174 nm, a 1:1 mixture of copperphthalocyanine and epoxypropyltriethoxysilane was coated on the surfaceof the electrode for the hole injection transport layer 9 and this wasbaked at 200° C. to form a layer of thickness 50 nm. Next, the firstcompound was printed in the form of a solution and dried to a filmthickness of 40 nm as the light emitting layer 2. More of the firstcompound was then formed into a film by being discharged within thebanks in the form of a solution using the ink-jet method and dried.Next, an Mg:Ag (10:1) alloy was EB vapor deposited, vapor deposited orsputtered on to form the cathode 1. Finally, the electroluminescentelement was molded under an inert gas in a degassed epoxy resin as ameans of isolating it from the surroundings.

Polyvinylcarbazole was used for the first compound in the blue lightemitting picture elements, but DPVBi, 1,1,4,4-tetraphenylbutadiene,oxadiazole, azomethine zinc complex, BA1q and derivatives of thesecompounds can be used. Furthermore, a mixture with Alq3 (ChemicalFormula 9) as a dopant can be used in a green light emitting pictureelement and coumarin 6, for example, can be admixed as a dopant for ablue-green light emitting substance. Furthermore,poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) can beadmixed as a dopant in a red light emitting picture element. SCM1 andNile Red, for example, can be admixed as dopants in a blue-green lightemitting picture element.

The same effects can be realized even if active elements such as TFTelements are formed for forming the anode and high capacity displays arepossible.

Materials which have a low work function can be used instead of Mg:Agfor forming the cathode and, for example, magnesium, aluminum, andalkali and alkaline earth metals such as lithium and calcium, and alloysin which these metals are used, can be used for this purpose.

Embodiment 8

This embodiment is an example in which the surfaces of theelectroluminescent elements made in embodiment 1 to 7 are subjected toan anti-glare treatment and/or an anti-refection treatment.

On sticking a “Non-glare Sheet AG20” manufactured by the Nitto Denko Co.onto the transparent substrates shown in the embodiments, reflectionswere greatly reduced and visibility was improved. Furthermore, onapplying an anti-reflection coat to the Non-glare sheet the reflectionswere virtually eliminated and visibility was improved.

Provided that they has a similar effect, all anti-glare sheets can beused in the same way. Furthermore, multi-layer coatings which havelayers which have different refractive indices, and coating withmaterials which have a low refractive index, and especially withfluorinated polymers such as “Saitoppu” (manufactured by the Asahi GlassCo.) for example, can also be used as anti-reflection coats.

Embodiment 9

An example in which an electroluminescent element of the invention isprovided with a simple matrix drive is shown in this embodiment. Asimple connection chart for the drive circuit and the electroluminescentelement is shown in FIG. 8. As shown in FIG. 8, said display apparatusincludes; the electroluminescent element 12, a scanning electrode driver13, a signal electrode driver 14 and a controller 15. Theelectroluminescent element 12 is an element as manufactured in any ofthe abovementioned embodiments. The anode and cathode are formed as arectangular array of anodes and cathodes, which are connected in the wayindicated in FIG. 8. The scanning electrode driver 13 is the driverwhich specifies the drive element in the vertical direction of thescreen. The signal electrode driver 14 is the driver which specifies thedrive element in the horizontal direction of the screen. The controller15 controls the overall picture element drive by supplying scanningelectrode signals and signal electrode signals to the aforementioneddrivers.

The drive waveform which the controller 15 applies to the anode and thecathode is shown in FIG. 9. In FIG. 9, Tf shows the time for one scan.Here it is being driven at 1/100 duty. With this drive waveform awaveform with a pulse width which matches the steps to be displayed isapplied to the selected picture element at an adequate voltage Vs for itto emit light. When an electroluminescent element of Embodiment 1 isbeing used a brightness of 100 cd/m² was obtained at a drive voltage of20 V when coumarin 6 was being used for the second compound.

With the abovementioned invention it is possible to realizeelectroluminescent elements which are bright and which have highcontrast by means of a very simple construction with anelectroluminescent element in which a light emitting element andfluorescent conversion materials are combined. Furthermore, highperformance electroluminescent elements can be manufactured cheaply bymeans of a very simple process. Consequently the invention can beapplied to cheap portable-type terminals and displays use on vehicles.

What is claimed is:
 1. A method for manufacturing an electroluminescentelement having an anode, a cathode and a light emitting layer disposedin a plane between the anode and the cathode, wherein the method forforming the light emitting layer comprises: forming a first layercontaining a fluorescent first compound; forming a second layercontaining a second compound which absorbs a first fluorescence emittedby the first compound and which emits a second fluorescence of a longerwavelength than the first fluorescence; and allowing the second compoundto permeate into the first layer to form a portion where theconcentration of the second compound has a gradient along a thicknessdirection of the light emitting layer perpendicular to the plane,wherein the second layer is formed using an ink-jet method.
 2. A methodfor manufacturing an electroluminescent element having an anode, acathode and a light emitting layer disposed in a plane between the anodeand the cathode, wherein the method for forming the light emitting layercomprises: forming a first layer containing a fluorescent firstcompound; forming a second layer containing a second compound whichabsorbs a first fluorescence emitted by the first compound and whichemits a second fluorescence of a longer wavelength than the firstfluorescence; and allowing the second compound to permeate into thefirst layer to form a portion where the concentration of the secondcompound has a gradient along a thickness direction of the lightemitting layer perpendicular to the plane, wherein the first layer isformed using an ink-jet method.
 3. A method for manufacturing anelectroluminescent element having an anode, a cathode and a lightemitting layer disposed between the anode and the cathode, comprising:forming a first layer containing a first compound; and forming a secondlayer containing a second compound which absorbs a first light emittedby the first compound and emits a second light of a longer wavelengththan the first light, the second layer formed by an ink-jet method. 4.The method of claim 3, wherein the second layer is formed after thefirst layer.
 5. The method of claim 3, wherein the second layer isformed before the first layer.
 6. The method of claim 3, wherein thefirst layer is formed using an ink-jet method.
 7. The method of claim 3,further comprising forming a hole injection transport layer over theanode.
 8. The method of claim 3, wherein the first and/or the secondlayer is formed into picture elements, the method further comprisingforming banks between the picture elements.